X-ray CT apparatuses are for obtaining a tomographic image of a subject from attenuation when X-rays generated from an X-ray tube pass through the body of the subject, and a technique called photon counting has been proposed to distinguish and detect energy of individual X-rays at each pixel of a detector.
In imaging by X-rays, the number of radiation generation is larger than that of inspection for nuclear medicine etc., and a counting rate in a detector is high. For this reason, it is necessary to lower the counting rate per pixel by downsizing detector pixels. In ordinary X-ray CT detectors, detectors are arranged at a pitch of about 1 mm. In photon counting CT which counts the number of photons, however, it is necessary to miniaturize detectors to a pitch of 0.5 mm to 0.05 mm. However, when detector pixels are miniaturized, phenomena such as detection of X-rays divided to a plurality of detector pixels due to occurrence of characteristic X-rays, Compton scattering, or the like or charge sharing where an electron cloud generated by X-rays spreads over two pixels occur at the time of X-ray detection. When these phenomena occur, an event originally to be detected as one high energy is observed as two low energy events. Since such erroneous detection deteriorates an image, erroneous detection has to be removed.
As a method of detecting such erroneous detection, there is a method of processing scattered radiation in a detector as described in PTL 1. By such a method, it is possible to process divided signals in the detector.